The present invention relates to X-ray tubes and in particular to controlling the amount of heat produced in the tube housing.
It is known to provide an X-ray tube which comprises an electron emitter and a metal anode where the anode is held at a positive potential (say 100 kV) with respect to the electron emitter. Electrons from the emitter accelerate under the influence of the electric field towards the anode. On reaching the anode, the electron loses some or all of its kinetic energy to the anode with over 99% of this energy being released as heat. Careful design of the anode is required to remove this heat.
Electrons that backscatter from the anode at low initial energy travel back down the lines of electrical potential towards the electron source until their kinetic energy drops to zero. They are then accelerated back towards the anode where their kinetic energy results in generation of further heat (or X-radiation).
Electrons that scatter from the anode at higher energies can escape the lines of electrical potential that terminate at the anode and start to travel towards the tube housing. In most X-ray tubes, the electrons can reach the housing with high kinetic energy and the localised heating of the housing that results can lead to tube failure.